do weekly waterchanges, feed him a good quality pellet like hikari gold, that naturaly enhance colour, and because of the weekly water changes u can feed him more,
which means his growth rate will go up and he will develope more colour etc as he does
forget the flakes and feed some NLS along with krill and other frozen foods, your dempsey will color up nicely, as long as the water conditions are good of course
just addded a black garbage bag to the 29 as a back ground and now ecerything seems brighter and thefish seem to like it more. and looks like my male and female pink con in there 10 has made a nest under a ornament so soon hoply i see some free feeders and a few keeper baby pink con, and im also hoping they produce black con frys.